1. Field of the Invention
The present invention relates to a material for the preparation of internal-finishing skin of a composite resin type, which comprises a polyurethane type resin (hereinafter referred to as "PU") having a specified chemical structure and a specified composition, and a polyvinyl chloride type resin (hereinafter referred to as "PVC"). More particularly, the present invention relates to a material for the preparation of an interior-finishing skin superior in flexibility, anti-fogging properties, adhesiveness to a cushioning material, non-surface tackiness, heat resistance, impact strength at low temperature, and having satisfactory embossing property for surface decorative design.
2. Related Background Art
In recent years, requirements for the performance of internal-finishing skin are becoming increasingly higher and severer. The internal-finishing skin is required to be satisfactory in both of touch feeling and design decorativeness in addition to the properties as an internal-finishing skin.
Particularly in the skin for automotive internal-finishing, performance requirements have become much severer: namely requirements for flexibility to give soft touch feeling, and simultaneously, with regard to durability, long-term retention of properties at high temperature and impact resistance at low temperature are required. Further, anti-fogging properties are important from the standpoint of safety.
On the other hand, the requirement for workability of the materials for the preparation of internal-finishing skin is becoming severer for higher production efficiency: the embossing should be satisfactory in skin material molding, and surface pattern should be retained without loss of emboss at release of mold even at a high temperature. The surface emboss pattern has become greatly complicated in these days for higher decorativeness of design, for which a finely designed and deeply embossing mold has to be employed, so that the aforementioned requirements for workability are becoming severer.
Under such circumstances, non-rigid PVC resins plasticized with a plasticizer are mainly used conventionally for automotive internal-finishing skin. Such a non-rigid PVC, which contains a low molecular plasticizer, has a disadvantage of impairing driver's visual range owing to oil film formation (fogging) on a windshield or the like caused by migration of the plasticizer. Additionally, the non-rigid PVC has disadvantages, caused by migration of a plasticizer, of disappearance of embossing, hardening to become brittle, and occurrence of cracking by impact at a low-temperature.
Increase of softness to meet the requirement for soft feeling needs an increased amount of the plasticizer, which results in more serious disadvantages mentioned above, and low mechanical properties to cause loss of emboss on hot molding.
Hitherto, the purpose of offsetting the above disadvantages, it is known that polymer alloys are produced by blending or copolymerizing PU and PVC for preparing non-rigid PVC.
For a material for the preparation of automotive internal-finishing skin, however, the conventional PU-PVC composite resins have not been brought into practical use because of incompatibility of flexibility for soft touch feeling and mechanical properties of the product, and moldability for embossing and mold releasability during processing the material for internal-finishing skin, especially in large-sized molded articles such as skins for an instrument panel.
Japanese patent laid-open application Sho 62-64861 discloses a composite resin composition composed of PU and PVC, in which the PU is prepared by reaction of an organic polyisocyanate with a polyesterpolyol derived from 3-methyl-1,5-pentanediol solely or a mixed diol containing it at a content of 10 mole % or more with a dicarboxylic acid. The PU-PVC composite resin composition thus prepared is known to be satisfactory in compatibility of PU with PVC, to exhibit sufficient plasticizing property, and to prepare a composition for soft articles with easy.
Practicably, however, if the content of 3-methyl-1,5-pentanediol in the mixed diol is 30 mol % or less, the PU derived from the mixed diol cannot exhibit satisfactory plasticizing property. If the content exceeds 30 mol %, the PU-PVC composite resin composition has tackiness and is liable to cause inconveniences during processing such as loss of emboss in molding and the like. Accordingly, in the mixed diol, a linear diol having relatively many methylene groups such as 1,9-nonanediol and the like is incorporated as one component. In this case, however, disadvantages arise that the plasticizing effect is not sufficiently exhibited and processing temperature at the hot molding becomes high to reduce the moldability. Accordingly, this PU-PVC composite resin composition, in use for internal-finishing sheets, is disadvantageous in difficulty of the preparation of embossing and of article having fine decorative design.
As described above, improvement in soft touch feeling or flexibility of a thermoplastic resin will impair tensile strength, heat distortion resistance and other properties thereof, and will increase surface tackiness properties of the sheets. It is difficult that known resins can be formed into a sheet having a sufficiently decorative design of skin of a leather-like pattern without loss of emboss during heat molding or without sticking to a mold.